/*
*Copyright (c) 2021, Alibaba Group;
*Licensed under the Apache License, Version 2.0 (the "License");
*you may not use this file except in compliance with the License.
*You may obtain a copy of the License at

*   http://www.apache.org/licenses/LICENSE-2.0

*Unless required by applicable law or agreed to in writing, software
*distributed under the License is distributed on an "AS IS" BASIS,
*WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
*See the License for the specific language governing permissions and
*limitations under the License.
*/

/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you under
 * the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
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/*
 * Modifications Copyright Havenask Contributors. See
 * GitHub history for details.
 */

package org.havenask.geometry.utils;

/**
 * Utilities for common Bit twiddling methods. Borrowed heavily from Lucene (org.apache.lucene.util.BitUtil).
 */
public class BitUtil {  // magic numbers for bit interleaving
    private static final long MAGIC[] = {
        0x5555555555555555L, 0x3333333333333333L,
        0x0F0F0F0F0F0F0F0FL, 0x00FF00FF00FF00FFL,
        0x0000FFFF0000FFFFL, 0x00000000FFFFFFFFL,
        0xAAAAAAAAAAAAAAAAL
    };
    // shift values for bit interleaving
    private static final short SHIFT[] = {1, 2, 4, 8, 16};

    /**
     * Interleaves the first 32 bits of each long value
     *
     * Adapted from: http://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
     */
    public static long interleave(int even, int odd) {
        long v1 = 0x00000000FFFFFFFFL & even;
        long v2 = 0x00000000FFFFFFFFL & odd;
        v1 = (v1 | (v1 << SHIFT[4])) & MAGIC[4];
        v1 = (v1 | (v1 << SHIFT[3])) & MAGIC[3];
        v1 = (v1 | (v1 << SHIFT[2])) & MAGIC[2];
        v1 = (v1 | (v1 << SHIFT[1])) & MAGIC[1];
        v1 = (v1 | (v1 << SHIFT[0])) & MAGIC[0];
        v2 = (v2 | (v2 << SHIFT[4])) & MAGIC[4];
        v2 = (v2 | (v2 << SHIFT[3])) & MAGIC[3];
        v2 = (v2 | (v2 << SHIFT[2])) & MAGIC[2];
        v2 = (v2 | (v2 << SHIFT[1])) & MAGIC[1];
        v2 = (v2 | (v2 << SHIFT[0])) & MAGIC[0];

        return (v2<<1) | v1;
    }

    /**
     * Extract just the even-bits value as a long from the bit-interleaved value
     */
    public static long deinterleave(long b) {
        b &= MAGIC[0];
        b = (b ^ (b >>> SHIFT[0])) & MAGIC[1];
        b = (b ^ (b >>> SHIFT[1])) & MAGIC[2];
        b = (b ^ (b >>> SHIFT[2])) & MAGIC[3];
        b = (b ^ (b >>> SHIFT[3])) & MAGIC[4];
        b = (b ^ (b >>> SHIFT[4])) & MAGIC[5];
        return b;
    }

    /**
     * flip flops odd with even bits
     */
    public static final long flipFlop(final long b) {
        return ((b & MAGIC[6]) >>> 1) | ((b & MAGIC[0]) << 1 );
    }
}
